Loop B Serine phosphorylation status differentially affects pH sensing of PIP aquaporins

AGUSTIN YANEFF; LORENA SIGAUT; ALIAGA FANDIÑO CECILIA; ALLEVA KARINA; LIA PIETRASANTA; AMODEO GABRIELA

Sierra de la Ventana

Congreso; XLIII Reunión Anual de la Sociedad Argentina de Biofisica; 2014

Sociedad Argenina de Biofísica

The crystallization of SoPIP2;1 in an open and close conformation as well as biophysical evidences have allowed to propose a gating mechanism in PIP aquaporins. A close state seems to prevail under different stimuli: cytosolic pH decrease2 , intracellular Ca2+ concentration increase and desphosphorylation of specific serines1 . In previous work, we characterize FaPIP1;1 and FaPIP2;1 in terms of their Pf and pH inhibition response and demonstrate that heterotetramerization affects pH gating sensitivity2 . In the light of these findings we decided to explore if phosphorylation of specific residues is involved in this response. Several PIP2 mutants where Serine from the loop B was replaced to alanine showed less activity as water channels when expressed in Xenopus laevis oocytes3?5 or yeast6,7. However, for several plant species, loop B serine has shown to be non-phosphorylated in vivo4,5,8. In this work, we generate loop B mutants (FaPIP2;1S121A and FaPIP1;1S131A) in order to simulate desphosphorylated state and characterize their behavior in terms of Pf and pH inhibition response. Our results show that loop B serine phosphorylation status affects pH gating sensitivity for FaPIP2;1 but not for FaPIP1;1. Thus, we propose a crosstalk between different regulatory mechanisms (heterotetramerization, serine phosphorylation status and pH sensitivity) that would rule the Pf of a membrane that express PIPs